The present disclosure relates generally to glucose sensors. In particular, the present disclosure relates to non-enzymatic glucose sensors and methods for fabricating the same.
Diabetes mellitus is a metabolic disorder that results from insulin deficiency and is reflected by blood glucose concentrations being outside the normal range of 80-120 mg/dL. Diabetes causes complications such as neuropathy, nephropathy and retinopathy which result in heart disease, kidney failure, or blindness, respectively. Therefore, in order to treat diabetes, it is very important for diabetics to control their blood glucose levels by conducting self-monitoring several times a day. A wide variety of methods for glucose analysis, including electrochemistry, near infrared spectroscopy, optical rotation and the like, have been reported in the literature.
The most commonly used technology for blood glucose determination is an enzyme based method. The enzymatic glucose sensors have a serious drawback of oxygen dependence. The errors emanating from this high dependence on oxygen to mediate regeneration of the catalytic center are quite significant as oxygen levels in blood vary considerably. Often enough oxygen is not available in a real blood sample to efficiently maintain glucose oxidation, thus this oxygen deficit has a great impact on accurate determination of glucose levels. The enzyme based glucose sensors also encounter problems in terms of the stability of the enzyme, the role of the mediator, enzyme leaching etc.
Though enzymatic glucose sensors are extensively studied and applied, one problem with these sensors is their short shelf life, which originates from the intrinsic nature of the enzymes. Further, a complicated procedure, including processes such as adsorption, cross-linking, entrapment, and electropolymerization, is required for the immobilization of the enzyme on the solid electrode, and this may decrease the activity of the Glucose oxidase. Since the sensitivity of these glucose sensors essentially depends on the activity of the immobilized enzymes, reproducibility is still a critical issue in quality control.
To overcome the above mentioned problems associated with the enzymatic glucose sensors, the use of alternative co-substrates emerged. Synthetic, electron-accepting mediators are utilized to facilitate electron transfer and their subsequent re-oxidation on the electrode resulting in a quantifiable amperometric current. A number of non-physiological mediators have been reported including ferrocene derivatives and ferricyanide of which most commercial sensors use quinines and transition-metal complexes. Several problems still remain when using a mediator. Maintaining the mediator molecules, which are small and diffusive in nature, near the electrode and on the enzyme surface is very difficult, particularly over prolonged use and that creates a need for elaborate and complicated methods of tethering the mediator to the two entities. Although the mediator ideally reacts with the enzyme at a considerably faster rate than oxygen, the possibility of dissolved oxygen also competing with the mediator is highly likely, thus reducing the efficiency of the system and causing a buildup of hydrogen peroxide. It is also possible for the mediator to react with interfering species present in the blood, further affecting the accuracy and efficiency of the analytical system.
Three essential requirements for a material having good sensor characteristics are sensitivity, selectivity and mechanical stability. Components chosen for the fabrication of the sensor electrode should satisfy these three requirements. Furthermore, the sensor electrode fabrication processes should be reproducible and able to be applied for commercial purposes in a simple manner.
Therefore there is a need for glucose sensing technology having sensors with high degree of selectivity and sensitivity and stable at wide range of temperature/humidity, as proposed herein.